Single horizontal well gravity oil drainage production device and method of using downhole steam generation

ABSTRACT

The invention relates to a single horizontal well gravity oil drainage production device and method of using downhole steam generation. The continuous coiled tubing string is lowered into a horizontal well, the combustion aided agent, fuel and water are sent downhole through corresponding paths to be heated to the supercritical state of water by the preheater. Continuous combustion is conducted in the steam generator to produce water vapor and carbon dioxide. Steam is injected into an oil formation through a steam generator outlet, and heated crude oil and steam condensate water enter the horizontal well downward and flow into the oil production pump to be lifted to the ground. The single horizontal well gravity oil drainage production device and method are reliable in principle, steam injection and oil production lifting work cooperatively in the same horizontal well, saving production cost.

CROSS-REFERENCE TO RELATED APPLICATION AND CLAIM TO PRIORITY

This application is related to Chinese Patent Application No. 201910435701.0 filed May 23, 2019, the disclosure of which is incorporated herein by reference and to which priority is claimed.

FIELD OF THE INVENTION

The invention relates to the field of oil production, and relates to a device and method for improving oil well production and the rate of crude oil recovery, in particular to a single horizontal well gravity oil drainage production device and method of using downhole steam generation.

BACKGROUND OF THE INVENTION

Steam Assisted Gravity Drainage (SAGD) is an advanced technology for heavy oil production. It is a method of oil production that focuses on the role of gravity drainage by reducing the viscosity and increasing the mobility of crude oil by heating the oil formation with vaporized latent heat from injected steam. During gravity oil drainage production, steam is injected into the oil reservoir from a horizontal injection-production well or from several vertical steam injection wells located above a horizontal production well near the bottom of the reservoir. The heated crude oil and steam condensate are produced from the horizontal production well located at the bottom of the oil reservoir. This method can greatly increase the production and recovery factor of heavy oil.

In order to save drilling capital, one single horizontal well can be used instead of dual horizontal wells for SAGD production. However, steam injection and oil production on the same well can cause the high temperature of the steam injection string to reheat the liquid produced, resulting in flash evaporation of the output liquid, severely interfering with the normal operation and production of the oil production pump. In fact, only half of the horizontal wells are working normally, which is difficult to control and inefficient. The fundamental problem is that steam is injected from the surface along the wellbore into the formation, which inevitably causes high temperatures in the wellbore and the secondary heating of the liquid produced from the same wellbore. This often causes the liquid at the pump to flash, and low efficiency.

SUMMARY OF THE INVENTION

The invention relates to a single horizontal well gravity oil drainage production device and method of using downhole steam generation. High-temperature steam is generated at the bottom of the well, and the oil formation has high heating efficiency. Low-temperature water, which is injected along the upper wellbore, exchanges heat with the liquid produced. The temperature of the liquid produced at the pump can be controlled to be much lower than the saturation temperature of the steam, which improves the efficiency of the oil production pump.

An object of the invention is to provide a single horizontal well gravity oil drainage production device using downhole steam generation. The device is reliable in principle and is simple in operation. Steam injection and oil production lifting are realized in the same horizontal well, and production costs are saved, which is beneficial to efficient production of heavy oil reservoirs.

Another object of the invention is to provide a single horizontal well gravity oil drainage production method using the above device. The method uses a downhole steam generator to inject steam in a horizontal well located near the bottom of the oil formation, and uses the gravity oil drainage process of lifting the heated crude oil and steam condensate with an oil production pump, which is not limited by the depth of the oil formation, effectively promotes the development of steam injection in heavy oil reservoirs and has broad industrial application.

To achieve the above objectives, the invention provides the following solutions.

A continuous tubing string made of multiple continuous coiled tubes is placed in a horizontal well. The combustion aided agent, fuel and water are transported downhole, preheated, and ignited downhole to produce continuous supercritical water vapor (steam) and carbon dioxide, and enter the oil well through the control of the exit. The required ratio of water vapor and carbon dioxide gas are controlled. The steam vapor moves upward in the near-well zone to form a steam chamber. The crude oil heated by the steam chamber flows downward, and the steam vapor condenses into water, which also moves downward. The liquid reservoir driven to the horizontal well by gravity flows continuously to the oil production pump and is lifted to the surface. By controlling the amount of water injected and produced as well as the heating power, the pressure of the steam chamber is adjusted. Because the invention generates steam at the bottom of the well, it has high thermal efficiency and can be applied to very deep heavy oil reservoirs.

The single horizontal well gravity oil drainage production device using downhole steam generation comprises a high-temperature-resistant dual-string injection-production well head assembly, and a downhole steam generation and injection system and an oil production lifting system that are lowered through the wellbore.

The steam injection system comprises a continuous coiled tubing, a water tank, a fuel tank, a combustion aided agent tank, a preheater, an igniter, a steam generator, a power supply, and a test signal receiver. The continuous coiled tubing string comprises a path for conveying the combustion aided agent, fuel, and water, and a path for conveying power and receiving test signals. The continuous coiled tubing string is lowered into the horizontal well through the injection-production well head, is connected to the water tank, the fuel tank, and the combustion aided agent tank on the ground, and is connected to the preheater, the igniter, and the steam generator in a downhole liner in order. The continuous coiled tubing string is further connected to the power supply and the test signal receiver located on the ground.

The oil production lifting system comprises an oil tube and an oil production pump. The oil production pump may be a sucker-rod pump or a rodless pump such as an electric submersible pump, depending on the conditions of the well.

According to the single horizontal well gravity oil drainage production method using the above device, the process is as follows: the continuous coiled tubing string is lowered into the horizontal well through an injection-production well head, the combustion aided agent, fuel and water are sent downhole through corresponding paths of the continuous coiled tubing string after being pressurized, respectively, heated to the supercritical state of water by the preheater, mixed and ignited, continuous combustion is conducted in the steam generator to produce water vapor and carbon dioxide, steam is injected into an oil formation through a steam generator outlet to form a steam chamber, and heated crude oil and steam condensate water enter the horizontal well downward and are lifted to the ground by continuously flowing into the oil production pump. The temperature and pressure of the well are transmitted to the test signal receiver on the ground through the continuous coiled tubing string, the continuous operation of the downhole steam generator and the control of the operating parameters of the oil production process are realized through ground regulation, and steam injection and oil production lifting working cooperatively in the same horizontal well.

In the invention, the steam is generated from the process that organic fuel is in a chemical reaction with oxygen under supercritical conditions of water, and generates carbon dioxide and water during combustion, which is accompanied by a large amount of heat release, the continuously entering fuel makes the supercritical state persist, and the newly entering water continues to be converted into steam, thereby achieving continuously generating high-temperature steam.

In the invention, the steam is injected into the oil formation through the outlet of the steam generator. The steam first flows from the heel section of the horizontal section to its toe. During this process, the vapor phase portion of the steam continuously enters the oil formation and exchanges heat with the surrounding formation. Before reaching the toe, the vapor phase portion of the steam is exhausted, leaving only condensate water. The vapor phase portion of the steam entering the oil formation upwards forms a steam chamber. The heated crude oil and steam condensate water enter the horizontal well downward and are lifted to the ground by continuously flowing into the oil production pump.

In the invention, the continuous operation of the downhole steam generator and the control of the operating parameters of the oil production process are realized through ground regulation, referring to the production method in which the injection and production process is regulated in accordance with the temperature and pressure controls required by the downhole steam-assisted gravity oil drainage to achieve the simultaneous operation of steam injection and oil production in the full horizontal section of the same well.

The invention can precisely control the amount of liquid produced and also the amount of steam injected, so the pressure in the steam chamber can be controlled. The invention can be applied to oil reservoirs with a well depth of 1,000-3,000 meters or even at depth of more than 3,000 meters.

By controlling the rate of injecting liquid and producing liquid and the operation procedures of the steam generator, the invention can carry out an oil production method with intermittent injection and production modes as required.

The combustion aided agent, fuel, oxygen, and injected water are mixed according to a certain ratio and injected into the well. After combustion, different ratios of nitrogen and carbon dioxide can be obtained, which meets the needs for improving development efficiency in different development stages.

The invention uses the above injected cold medium to perform heat exchange with the high-temperature liquid produced, reduces the temperature of the liquid produced, and ensures that the liquid produced has a large degree of subcooling before entering the pump, so that the oil production pump does not flash in the suction process and can accurately control the temperature of the liquid produced and pump efficiency in real time. At the same time, the injection medium is heated up, and a large amount of thermal energy is not lost to the ground, which increases the temperature of the liquid at the inlet of the downhole steam generator and further improves the thermal efficiency of the steam generator.

In the invention, both the downhole steam generation system and the oil production lifting system are lowered into the same horizontal well and work synchronously and cooperatively. This is different from the traditional dual-well SAGD, where two parallel horizontal wells are required. It is also different from the traditional single horizontal well SAGD, where the steam is generated from the ground and re-injected into the oil formation and it is difficult to control downhole steam quality and the oil production efficiency is low. It is different from the traditional steam generation manner, where the steam does not contain CO₂ and other gaseous media that are beneficial to improving oil displacement efficiency.

Compared with the existing ground steam injection thermal production method, the device and method of the invention have the following beneficial effects:

1) It is not limited by the depth of the oil formation and can be used for steam injection development of heavy oil reservoirs with a well depth of 1,000-3,000 meters or even deeper.

2) Compared with the dual-horizontal well SAGD, it saves half of the drilling cost, and saves the production cycle of preheating, which is more energy-saving and environmentally friendly.

3) The CO₂ generated during the combustion process enters the oil reservoir, which helps the development and expansion of the vapor cavity and provides additional oil displacement energy.

4) The use of cold medium injection provides a cooling process, which not only controls the flow of injected steam and produced liquid, but also controls the flashing of water produced and the plunging of steam into the oil production lifting system, which affects the normal operation of the pump. Therefore, the steam in the entire horizontal section is evenly distributed, the oil formation is used uniformly, and the horizontal section is highly used.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic structural diagram of a single horizontal well gravity oil drainage production device using downhole steam generation.

In the FIGURE, the reference numbers correspond to the following:

1—a dual-tube injection-production well head; 2—a casing; 3—a moving liquid level; 4—a tube; 5—an oil production pump; 6—a continuous coiled tubing string; 7—a hanger; 8—the produced liquid flow direction; 9—the injection steam direction; 10—a steam chamber; 11—a liner; 12—a preheater; 13—an igniter; 14—a steam generator; 15—a steam outlet; 16—a water tank; 17—a test signal receiver; 18—a power supply; 19—a combustion aided agent tank; 20—a fuel tank; 21—a pump.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT(S)

The invention is further described below with reference to the accompanying drawing, related description, and example, so that those skilled in the art can understand the invention. However, it should be clear that the invention is not limited to the scope of the specific embodiments. For those of ordinary skill in the art, various changes are included as long as they fall within the spirit and scope of the invention as defined and determined by the appended claims.

Referring to FIG. 1, the single horizontal well gravity oil drainage production device using downhole steam generation comprises a high-temperature-resistant dual-tube injection-production well head of a horizontal well, and a downhole steam generation and injection system and an oil production lifting system that are lowered through the well head, respectively.

The steam injection system consists of a continuous coiled tubing string 6, a water tank 16, a fuel tank 20, a combustion aided agent tank 19, a preheater 12, an igniter 13, a steam generator 14, a power supply 18, and a test signal receiver 17. The continuous coiled tubing string 6 comprises a path for conveying the combustion aided agent, fuel, and water, and a path for conveying power and receiving test signals. The continuous coiled tubing string 6 is lowered into the horizontal well through the injection-production well head 1, is connected to the water tank 16, the fuel tank 20, and the combustion aided agent tank 19 through the pump 21 on the ground, and is connected to the preheater 12, the igniter 13, and the steam generator 14 in a downhole liner (fixed by a hanger 7) in order. The continuous coiled tubing string 6 is further connected to the power supply 18 and the test signal receiver 17 located on the ground.

The oil production lifting system comprises an oil tube 4 and an oil production pump 5. The oil production pump 5 may be a sucker-rod pump or a rodless pump such as an electric submersible pump, depending on the conditions of the well.

The continuous coiled tubing string 6 is lowered into the horizontal well through an injection-production well head 1 and a casing 2, the combustion aided agent, fuel and water are sent downhole through corresponding paths of the continuous coiled tubing string 6 after being pressurized, respectively, heated to the supercritical state of water by the downhole preheater 12, mixed and ignited by the igniter 13, continuous combustion is conducted in the steam generator 14 to produce water vapor and carbon dioxide, steam is injected into an oil formation through a steam outlet 15 of the steam generator and then through a liner 11 (refer to FIG. 1 for the steam injection direction 9) to form a steam chamber 10, and heated crude oil and steam condensate water enter the horizontal well downward (refer to FIG. 1 for the produced liquid flow direction 8) and are lifted to the ground by continuously flowing into the oil production pump 5 such that a certain moving liquid level 3 is maintained.

EXAMPLE

The buried vertical depth of the oil formation is 2,500 meters, the length of the horizontal section is 400 meters, the net pay thickness is 30 meters, the permeability is 1 Darcy, the porosity is 25%, the viscosity of the degassed crude oil at 50° C. is 40,000 mPas, and the oil saturation is 60%. The formation pressure is 15 MPa.

A dual-tube well head can hold strings of a diameter of 140 mm and 70 mm, respectively. Two continuous coiled tubing strings of Ø 70 mm and Ø 25 mm are selected. A built-in cable and an electric heater of Ø 25 mm are installed, with sensors for testing also installed in the continuous coiled tubing string. There is a converting connector, a preheater, an igniter, a steam generator, and a steam outlet controller at the lower part. An oil production pump that matches the output of the well is selected. A low-temperature medium plunger pump with a working pressure of 35 MPa (suitable for three kinds of media) is selected, as well as supporting ground process flow, power supply, several material storage tanks, and a corresponding control system. Corresponding engineering parameters are determined according to the reservoir engineering design. The steam injection system is run in the downhole first and then the oil production system, which requires the cooperation of a continuous coiled tubing operating vehicle. 

What is claimed is:
 1. A single horizontal well gravity oil drainage production device using downhole steam generation, comprising a high-temperature-resistant dual-tube injection-production well head, and a downhole steam generation and injection system and an oil production lifting system that are lowered into the hole through the well head, wherein the steam injection system consists of a continuous coiled tubing string, a water tank, a fuel tank, a combustion aided agent tank, a preheater, an igniter, a steam generator, a power supply, and a test signal receiver, and the continuous coiled tubing string comprises a path for conveying the combustion aided agent, fuel, and water, and a path for conveying power and receiving test signals; wherein the continuous coiled tubing string is lowered into the horizontal well through the injection-production well head, is connected to the water tank, the fuel tank, and the combustion aided agent tank on the ground, and is connected to the preheater, the igniter, and the steam generator in a downhole liner in order; wherein the continuous coiled tubing string is further connected to the power supply and the test signal receiver located on the ground; and wherein the oil production lifting system comprises an oil tube and an oil production pump.
 2. The single horizontal well gravity oil drainage production device using downhole steam generation according to claim 1, wherein the oil production pump is a sucker-rod pump or an electric submersible pump.
 3. A single horizontal well gravity oil drainage production method using the device according to claim 1, wherein the process comprises the steps of: the continuous coiled tubing string is lowered into the horizontal well through an injection-production well head, the combustion aided agent, fuel and water are sent downhole through corresponding paths of the continuous coiled tubing string after being pressurized, respectively, heated to the supercritical state of water by the preheater, mixed and ignited, continuous combustion is conducted in the steam generator to produce water vapor and carbon dioxide, steam is injected into an oil formation through a steam generator outlet to form a steam chamber, and heated crude oil and steam condensate water enter the horizontal well downward and are lifted to the ground by continuously flowing into the oil production pump; the temperature and pressure of the well are transmitted to the test signal receiver on the ground through the continuous coiled tubing string, the continuous operation of the downhole steam generator and the control of the operating parameters of the oil production process are realized through ground regulation, and steam injection and oil production lifting work cooperatively in the same horizontal well.
 4. A single horizontal well gravity oil drainage production method using the device according to claim 2, wherein the process comprises the steps of: the continuous coiled tubing string is lowered into the horizontal well through an injection-production well head, the combustion aided agent, fuel and water are sent downhole through corresponding paths of the continuous coiled tubing string after being pressurized, respectively, heated to the supercritical state of water by the preheater, mixed and ignited, continuous combustion is conducted in the steam generator to produce water vapor and carbon dioxide, steam is injected into an oil formation through a steam generator outlet to form a steam chamber, and heated crude oil and steam condensate water enter the horizontal well downward and are lifted to the ground by continuously flowing into the oil production pump; the temperature and pressure of the well are transmitted to the test signal receiver on the ground through the continuous coiled tubing string, the continuous operation of the downhole steam generator and the control of the operating parameters of the oil production process are realized through ground regulation, and steam injection and oil production lifting work cooperatively in the same horizontal well.
 5. The single horizontal well gravity oil drainage production method according to claim 3, wherein the steam is generated from the process that organic fuel produces in a chemical reaction with oxygen under supercritical conditions of water, and generates carbon dioxide and water during combustion, which is accompanied by a large amount of heat release, the continuously entering fuel makes the supercritical state persist, and the newly entering water continues to be converted into steam, thereby achieving continuously generating high-temperature steam.
 6. The single horizontal well gravity oil drainage production method according to claim 4, wherein the steam is generated from the process that organic fuel produces in a chemical reaction with oxygen under supercritical conditions of water, and generates carbon dioxide and water during combustion, which is accompanied by a large amount of heat release, the continuously entering fuel makes the supercritical state persist, and the newly entering water continues to be converted into steam, thereby achieving continuously generating high-temperature steam.
 7. The single horizontal well gravity oil drainage production method according to claim 3, wherein the continuous operation of the downhole steam generator and the control of the operating parameters of the oil production process are realized through ground regulation, referring to the production method in which the injection and production process is regulated in accordance with the temperature and pressure control rule required by the downhole steam-assisted gravity oil drainage to achieve the simultaneous operation of steam injection and oil production in the full-horizontal well section of the same well.
 8. The single horizontal well gravity oil drainage production method according to claim 4, wherein the continuous operation of the downhole steam generator and the control of the operating parameters of the oil production process are realized through ground regulation, referring to the production method in which the injection and production process is regulated in accordance with the temperature and pressure control rule required by the downhole steam-assisted gravity oil drainage to achieve the simultaneous operation of steam injection and oil production in the full-horizontal well section of the same well.
 9. The single horizontal well gravity oil drainage production method according to claim 3, wherein the method is used for oil reservoirs with a well depth of 1,000-3,000 meters or a depth of more than 3,000 meters.
 10. The single horizontal well gravity oil drainage production method according to claim 4, wherein the method is used for oil reservoirs with a well depth of 1,000-3,000 meters or a depth of more than 3,000 meters.
 11. The single horizontal well gravity oil drainage production method according to claim 3, wherein an oil production method for intermittent injection can be carried out as required.
 12. The single horizontal well gravity oil drainage production method according to claim 4, wherein an oil production method for intermittent injection can be carried out as required. 